Re: [PATCH v5 11/60] target/riscv: vector integer add-with-carry / subtract-with-borrow instructions

[Richard Henderson]

On 3/12/20 7:58 AM, LIU Zhiwei wrote:
> +#define DO_MADC(N, M, C) ((__typeof(N))(N + M + C) < N ? 1 : 0)

Incorrect.  E.g N = 1, M = UINT_MAX, C = 1, adds to 1, which is not less than
N, despite the carry-out.

You want

    C ? N + M <= N : N + M < N

> +#define DO_MSBC(N, M, C) ((__typeof(N))(N - M - C) > N ? 1 : 0)

Similarly

    C ? N <= M : N < M


r~